Many industrial processes produce olefins that are mixtures of alpha olefins and internal olefins. Due to the similarities in properties between alpha and internal olefins of the same molecular weight or overlapping carbon numbers, it is not an easy matter to separate the two. Olefins are frequently used in the manufacture of polymers or as drilling mud additives, or as intermediates for the production of oil additives and detergents. Depending upon the particular application, it would be desirable to manufacture an alpha olefin composition having the greatest purity possible. For example, polyethylene polymers are often made by copolymerizing ethylene with small amounts of a linear alpha olefin such as 1-octene. A 1-octene olefin composition containing substantial branched species, especially on the second and/or third carbon atoms, is not suited for this purpose. The olefin needed for this purpose is one in which the branched alpha olefins are removed as much as possible. While such pure species of linear alpha olefins with a narrow carbon number range can be manufactured and provided at great cost, we have found that it would be particularly desirable to economically provide the application industry with large quantities of a purified linear alpha olefin composition made from a raw feedstock containing a mixture of at least internal olefins, linear alpha olefins, and 2-branched alpha olefins. Many feedstocks contain additional impurities such as alcohols, ketones, and 3-branched alpha olefins, from which the linear alpha olefins should be separated.
Separating and isolating linear non-branched alpha olefins from 2-branched alpha olefins and/or 3-branched alpha olefins is no easy task, especially when these species have similar or identical molecular weights or carbon numbers. Conventional distillation methods are inadequate to separate species of this type which have such closely related boiling points. The separation problem is further aggravated in that the linear non-branched alpha olefin species not only need to be separated from branched alpha olefins, but also from everything else present in the feedstock mixture, such as the internal linear or branched olefins. U.S. Pat. No. 4,946,560 described a process for the separation of internal olefins from alpha olefins by contacting a feedstock with anthracene to form an olefin adduct, separating the adduct from the feedstock, heating the adduct to produce anthracene and the olefin product enriched in alpha olefin, and separating out the anthracene from the alpha olefin. With respect to branched products, the patentee notes that the small amounts of branched products present in the feedstock will separate out in the same fashion as the internal olefins, that is, the alpha branched species will go with the alpha linear species, and be separated from the internal branched olefins which accompany the internal linear olefins, such that one obtains an alpha olefin composition and an internal olefin composition separated from each other in accordance with that invention. We have discovered, however, both the desirability to separate out linear alpha olefins from 2-branched alpha olefins and/or 3-branched alpha olefins in a raw feed stream containing these species and internal olefins, and the solution to this problem.